Thanks to the series' place in pop culture and the nature of the franchise, Back to the Future trilogy theories have popped up across the internet for years. It's no wonder Back to the Future is often regarded as one of the best '80s movies. Fans have written a George McFly theory about his belief that Marty is an alien, a Lorraine Baines theory about her dark past with Biff, and countless others. Although casual viewers may be unaware of this vast underworld, many passionate Back to the Future fans regularly comb the pages of Reddit to find the best Biff Tannen theory or dark Doc Brown theory.
Some of the most innovative notions use elements that occurred behind the scenes of the films, ultimately claiming them as canon. For example, one Marty McFly theory hypothesizes that actor Eric Stoltz - Marty's original actor who was ultimately replaced by Michael J. Fox - actually existed in the Back to the Future timeline. On a rainy day, try rewatching the Back to the Future films and see if the following fan theories hold water. And if you're a real BTF fan, beware of this list of Back to the Future plot holes that might ruin the whole series for you.